Silicon micromachined broad band light source

Abstract

A micro electromechanical system (MEMS) broad band incandescent light source includes three layers: a top transmission window layer; a middle filament mount layer; and a bottom reflector layer. A tungsten filament with a spiral geometry is positioned over a hole in the middle layer. A portion of the broad band light from the heated filament is reflective off the bottom layer. Light from the filament and the reflected light of the filament are transmitted through the transmission window. The light source may operate at temperatures of 2500 K or above. The light source may be incorporated into an on board calibrator (OBC) for a spectrometer.

What is claimed is:  
     
       1. A method comprising: 
       depositing a layer of silicon nitride on each of two faces of a first silicon substrate;  
       etching a cavity through the first silicon substrate and one of the silicon nitride layers to form a transmission window comprising silicon nitride;  
       forming a hole in a second silicon substrate;  
       depositing leads on either side of the hole;  
       positioning a filament comprising tungsten and having a spiral geometry across said hole;  
       connecting each of two ends of the filament to an associated one of the leads;  
       depositing a reflective film on one face of a third silicon substrate;  
       stacking the first, second, and third silicon substrates, in that order, and orienting said substrates such that the transmission window is positioned over the filament and the reflective film faces the filament; and  
       bonding the first, second, and third silicon substrates together.  
     
     
       2. The method of  claim 1 , further comprising: 
       depositing a bonding ring on a face of the first silicon substrate opposite the transmission window;  
       depositing a bonding ring on each of two faces of the second silicon substrate; and  
       depositing a bonding ring on the reflective film of the third silicon substrate.  
     
     
       3. The method of  claim 2 , further comprising providing an insulating layer between the leads on the second silicon substrate and the bonding ring on that face of said second substrate. 
     
     
       4. The method of  claim 1 , wherein the silicon nitride layers on the first silicon substrate are about 1000 Å thick. 
     
     
       5. The method of  claim 1 , further comprising depositing a 1000 Å layer of silicon nitride on each of two faces of the second silicon substrate. 
     
     
       6. The method of  claim 1 , wherein the filament has a thickness of at least about 10 μm.